Multimode waveguide termination



Oct- 21, 1969 w. SIMON 3,474,354

MULTIMODE WAVEGUIDE TERMINATION Filed March 29. 1967 INVENTOR WALTER SIMON DIRECTION OF fiRoPAs/moru BY ATTORNEY Fla 3 0? GENT United States Patent 3,474,354 MULTIMODE WAVEGUIDE TERMINATION Walter Simon, Silver Spring, Md., assignor to the United States of America as represented by the secretary of the Navy Filed Mar. 29, 1967, Sen-No. 627,588 Int. Cl. H01p 1/26 U.S. Cl. 33322 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention The present invention relates to waveguide terminations and more particularly to waveguide terminations which consist of a series of wire mesh grills.

The invention pertains to that field of the art wherein a waveguide system employs an attenuating means to dissipate the electro-magnetic energy passing along the waveguide.

DESCRIPTION OF THE PRIOR ART In the science of propagating electromagnetic energy passing through a waveguide there frequently arises the need for locating within the waveguide a load which will attenuate all of the energy being passed along the waveguide, thereby eliminating all reflections and standing waves within the waveguide. These waveguide loads, or terminations, take on a variety of configurations and are constructed of a number of different materials depending upon the amount of attenuation desired and the power involved. For example, many terminations in the past have been constructed of wedges of lossy material, placed in the waveguide at an appropriate angle to the axis of propagation, to absorb the mode of energy which is to be attenuated. Other terminations have taken the form of iris plates, or a conformal grating of wires, or the like, configured to conform or be parallel to the electric lines of force of the desired wave mode at the location of the grating. However, these prior art terminations have not been entirely satisfactory in completely attenuating the energy in the waveguide, and some even have adverse effects, as the iris plate, for example, which when inserted to introduce a reactance effect in the waveguide, acts as a generator of higher order waves than the one for which the reactive effect was desired. Wedges of lossy material likewise fail to fully attenuate all modes of energy for a complete termination.

SUMMARY OF INVENTION The present invention otfers material improvement over prior art waveguide loads by utilizing a plurality of metallic-wire grills which will provide maximum attenuation of the TE modes if the grills are placed vertically, and maximum attenuation of the TE modes if the grills are horizontal. Any number of grill cards may be used and each mesh is mounted on a dielectric card to enable rapid set-up and replacement. Since the grill mesh decreases in the direction of the propagation with the meshes getting smaller as distance from the source increases, the number of meshes being an exponential function of distance and being placed a distance apart equal 3,474,354 Patented Oct. 21, 1969 to approximately /1 of a wavelength at the highest frequency of interest, not only is essentially all of the power 1n the waveguide absorbed, but reflections and standing waves are virtually eliminated.

An object of the subject invention is the provision of a multimode waveguide termination.

Another object is the provision of a waveguide termination comprising a series of metallic wire grills.

Still another object is the provision of a waveguide termination wherein the mesh of the wire grills increases in density with distance from the source of energy.

Yet another object of the invention is the provision of a waveguide termination wherein the wire grills are spaced apart a distance equal to approximately of a wavelength at the highest frequency of interest.

Other objects and many of the attendant advantages of the present invention will readily become apparent as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a number of wire grills located inside a rectangular waveguide.

FIG. 2 shows a series of wire grills with varying density of wire mesh.

FIG. 3 shown an enlarged view of a typical wire grill.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, there is shown in FIG. 1 a rectangular waveguide 10 having a long side 11 and a shorter side 12, the direction of propagation of the electromagnetic energy within the waveguide being along the longitudinal axis thereof. Placed along the waveguide, transverse to the direction of propagation, are a plurality of grill cards 13, each card having an outer framework 14 made of a dielectric material which is used to support a number of parallel metallic wires 15. Contact is made between the ends of the grill wires 15 and the waveguide walls 11 or 12 by means of spring fingers (not shown), or any other form of electrical contact, so that each grill is grounded to the waveguide.

In applying the invention a series of the grill cards are utilized, with each having a different number of wires on the card, and therefore a different mesh, as shown in FIG. 2. In FIGS. 1 and 2 it will be observed that this series may run from n=1 to n=n, depending upon the amount of attenuation desired, as will be explained hereinafter.

In FIG. 3 there is shown, in an enlarged view, the relationship between the diameter of the grill wires and the spacing between them for a typical installation when the grill attenuates the TE modes of propagation.

The grills illustrated in FIGS. 1, 2 and 3 will provide maximum attenuation of the TE modes since the wires are vertical, while other cards, with horizontal wires, will provide maximum attenuation to the TE modes.

Turning now to the theory of operation behind the invention, it should be understood that energy propagating along the waveguide 10 gradually enters a medium of ever-increasing density. The grill wires 15 each absorb a slight amount of power from the field vector parallel to the grill and as the wave penetrates deeper into the mesh system, more and more grills are contacted and more and more power is absorbed from the wave.

Regardless of the mode, each wave, if penetration is deep enough, will encounter a sufiicient number of wires to attenuate the propagated power. The VSWR should be low in the attentuation band since in the region of highest power, that is in the low grid density region at the beginning of the meshes, there exists relatively few Wires or obstructions in the waveguide to distort the flow of energy and reflect power back to the source. In the region of higher density, reflection will increase, but this will be offset by the fact that the reflected energy must filter back through the mesh just penetrated to produce a VSWR in the input line. This additional journey back through the mesh will virtually eliminate reflection at the input.

As pointed out above, grill mesh dimension will decrease in the direction of propagation; that is, meshes get smaller as distance from the energy source increases, Thus, it has been determined experimentally that for complete attenuation the number of meshes will be an exponential function of distance from the power source and the meshes are placed a distance apart in the waveguide equal to approximately of a wavelength at the highest frequency of interest. Each mesh is individually mounted on a dielectric card to enable rapid set-up and replacement, thus, making it possible to mount any number of cards within the waveguide. The grills illustrated with the wire mesh running in a vertical direction will provide maximum attenuation of the TE modes. Other cards with the horizontal mesh will provide maximum attenuation of the TE modes.

From the above description of the structure and operation of the present device it is obvious that many improvements in the art of multimode waveguide terminations are offered by the invention. An inexpensive, easy to install, and completely effective attenuation device is disclosed by the multidensity, metallic-wire mesh, grill cards.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A multimode waveguide termination comprising:

a waveguide for the propagation of electromagnetic energy;

a plurality of dielectric frames located on the transverse axis of the waveguide with the plane of the frames facing the source of the energy; and

a plurality of metallic wires strung in equally spaced parallel relationship along each dielectric frame and wherein the spacing between the metallic wires on each of the dielectric frames gets smaller with each successive frame as the distance from the energy source increases.

2. The multimode waveguide termination of claim 1 wherein the number of metallic wires in the dielectric frames employed in the waveguide is an exponential function of the distance from the energy source.

3. The multimode waveguide termination of claim 2 wherein the distance between the dielectric frames is equal to of a wavelength at the highest frequency of interest.

4. The multimode waveguide termination of claim 3 wherein when the grill wires extend in a vertical direction across the waveguide maximum attenuation is offered to the TE modes and when the wires extend in a horizontal direction maximum attenuation is offered to the TE modes.

References Cited HERMAN KARL SAALBACH, Primary Examiner MARVIN NUSSBAUM, Assistant Examiner US. Cl. X.R. 333--81 

